3 ms·
The disk locality speed-up is increasingly not due to bandwidth, but latency (directly related to physical distance), which still matters. To provide some pers
by gtrubetskoy 11y ago
The disk locality speed-up is increasingly not due to bandwidth, but latency (directly related to physical distance), which still matters.
To provide some perspective - in 1 cycle of a 1GHz CPU light (or electric potential) travels about 30cm. So round-trip communication with a disk (or whatever) that is 5cm away vs one that is one 1m away (could be same rack) would take 20 times longer in each direction. Now consider communicating across a football-field-sized datacenter.
- wmf 11y agoI don't think the numbers support this. Mechanical disk latency is ~10ms while datacenter network latency is <100us, so the network contributes 1% extra latency. NVMe over fabrics is worse off because the flash latency is only ~100us and the network adds ~10us, but that's still nowhere near 20x.